BIOLOGICAL ASPECTS OF RESTING EGG DIAPAUSE AND HATCHING AND ITS APPLICATION TO MASS PRESERVATION TECHNOLOGY

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Diapause and hatching of the marine rotifer Brachionus plicatilis Muller resting eggs were examined. The total number of nuclei in an embryo during the internal diapause period increased from 22 on Day 2 post spawn to 39 (each n=1) on Day 6. The outer layr of embryo membrane gradually thickens from 1.2 (Day 0) to 4.0 mum (Day 8) (each n=10). Irradiation at more than 350 nm caused 1-25% hatching, but it reached 50-60% at 250-310nm light. The addition of hydrogen peroxide or prostaglandins (E1, E2 or F2 alpha) caused resting egg hatching even in darkness. The production of peroxide in seawater caused by light as well as the oxidation of fatty acid to prostaglandins inside the embryo is a possible mechanism of resting egg hatching.The hatchability of mass produced resting eggs (stored in sea water under the dark at 4ﾟC) gradually decreased due to bacterial infection of the porous egg surface. The canning method preserves eggs in a dry form, after lyophilization at -40oC.When partial pressures were less than 88 kPa, percent hatching after 6 months ranged between 16 and 20%, similar to that of uncanned eggs (19% hatching), but significantly lower (9 and 11%) at 88 and 101 kpa. Even after 12 months, percent hatching remained at 35% when canning was at 61 kpa. Canned eggs that were treated with NaClO (1ppm) or NFS-Na (5ppm) showed a significantly higher percent hatching (68% and 80%, respectively) than untreated eggs.